1. Field of the Invention
The present invention relates to the maintenance, repair, and use of archery bows, and more specifically compound bows. The invention is a portable bow press which allows the relief of tension on the bowstring on a high powered compound bow in order to facilitate repair, maintenance, aligning the pulleys, tightening the bowstring, stringing and unstringing of the bowstring and replacement of parts.
2. Description of the Related Art
Archery bows are a common tool of the hunter, sportsman, and warrior that have evolved over centuries. Artisans have constructed bows out of various materials, shapes and designs during this long history. Originally crafted in a single curve, bows have undergone many iterations including the long bow and recurve bow leading to today's most advanced compound bows. Compound bows differ from other bows in that they consist of multiple parts, including: a single riser made of a strong durable material with flexible limbs connected at either end of the riser to store the potential energy during draw. The bowstrings on a compound bow are connected indirectly to the limbs by means of pivoting eccentric pulleys (wheels or cams). Each pulley is connected towards the end of a limb with a rotation axis virtually perpendicular to the limb length.
Before the advent of the compound bow, maintenance and repair of simpler bows was accomplished by applying pressure to the outside of the limbs, forcing them inwards to create slack on the bowstring. Bows made of a single material could often be strung without the use of special equipment; the archer attaching one end of the string to a limb and exerting a force parallel to the bowstring. For instance see U.S. Pat. No. 3,416,220 to Richard I. Wilson disclosing the manual application of a bowstring to a single structure bow. This apparatus assists the archer in application of a force parallel to the bowstring to apply the string to the ends of the bow limbs. However, the methods that were commonly used to apply a bowstring to traditional bows are ineffective for the compound bows because of the stiffness of the compound bow limbs, additional force needed, and the complex mechanism and fine tuning requirement of the cams. Stringing and other maintenance on the compound bow cannot be easily accomplished without mechanical assistance.
Early bow presses consisted of large vice structures that would encompass and surround the entire bow and exert pressure from outside the bow to compress the limbs inward. Such vices are generally mounted to a floor within a workshop and are much too large for the hunter on the go. As an improvement to the vice, new mechanisms were invented to allow one to slacken and hold the bowstring while away from the workshop.
The ability to service a bow in the field is a highly desired feature in the archery market. Various portable mechanisms for stringing compound bows are disclosed. For example, U.S. Pat. Nos. 4,074,409; 4,291,452; 4,599,987; 4,846,142; 5,125,389; 5,606,963; 5,746,192; 6,957,647; 7,089,923 issued respectively to Jimmie T. Smith, Archie E. Whitman et al., Leonard D. Rezmer et al., Richard Tone, Edwin Paff, Paul J. Wenzel, Edward B. Gissel, Jeremy M. Evans et al., and Kenneth Johnson.
The '409 patent to Smith discloses an apparatus to assist in the changing of a bowstring on a compound bow. The '409 patent includes an auxiliary cord which connects directly to the bow cable above and below the string attachment elements. The cord is slidably connected to the bow cable at one end of an elongated handle, enabling the exertion of a force generally parallel to the bowstring to pull the distal ends of the limbs together to slacken the bowstring. The other end of the handle has an aperture through which the cord is placed to allow the handle to slide along the cord. The brackets set forth in the '409 patent connect directly to the bowstring, as an example of many of the portable bow press mechanisms.
The '452 patent to Whitman et al. also attaches a tension relieving apparatus directly to the bowstring. The '452 patent comprises an auxiliary cable, whose ends attach via clamp means to the bowstring between the cams.
The '923 patent to Johnson returns to the idea of the vice bow press with portable extending members that attach at the ends of limbs to provide pressure. The placement of the members provides for a safer tensioning system and allows easier draw due to the mechanical advantage of the extension.
The tensioning apparatus disclosed in U.S. Pat. No. 5,125,389 to Paff represents an improvement on the prior art by connecting a portable bow press temporarily in the space between split limbs on the compound bow. As compound bows have evolved to place the eccentric pulleys at the ends of the limbs, most modern compound bows feature a split limb with a eccentric pulley connected via an axle that runs between the two prongs of the split limb. The '389 patent takes advantage of this assembly by orienting an anchor within the limbs so as to apply pressure to the limbs directly, allow for easy attachment of the press, and leave the bowstring free for further manipulation. U.S. Pat. Nos. 5,746,192 and 6,957,647 contain the same anchor mechanisms as the '389 patent and offer improvements in the tightening mechanisms.
All technologies that place force directly to the limbs risk damage to the limbs as the limbs are not designed for force application at places other than the pulley axle. U.S. Pat. No. 5,606,963 overcomes this problem by applying the adjustment device to the pivot bore of the cam. Unfortunately, the apparatus disclosed in the '963 patent requires the application of the device within the space between the limb prongs and must be applied prior to the initial mounting of the pulleys and pulley axle. Additionally, this solution provides an inordinate amount of force off the center line of the bow limb that can cause an inequality in the forces and exert substantial torque on the limbs. This off-center force, and resulting torque, risks over stressing the limbs that may cause breaks along the limb.
The advent of the compound bow introduced a new and extraordinary amount of complexity into bow design. One of the main difficulties facing designers of these bows, is the calculation and adaptation of design to balance the torsional pulley forces expressed through the pulley axle on the bow limbs. Torque occurs as various forces pull on the limbs, and at the pulley(s). The translation of forces occurring at the pulley(s) causes smaller forces to be expressed along the bowstring and larger forces applied on cables that draw the limbs. The placement of the pulley and its various components in relation to the true center of the limbs is an important factor to combat the torque and its ill effects on compound bows. For instance, a wide-pulley design causes the maximum limb torque at rest, or zero draw, and a minimum torque at full draw. Diagonally-grooved-wide pulleys spread the two opposite forces on the limbs over zero- and full-draw, reaching a minimum torque as the bowstring is drawn (yolk-systems tend to deal with torque in a similar fashion). Narrow-eccentric pulleys with cable-guards tend to allow little torque at rest, and maximize torque at full draw. Misplaced, unusual, and strong torque is a major cause of bow wear and tear and can often lead to cracking of limbs, both horizontally and vertically.
No prior art bow press has completely accommodated the torque issues by allowing a bow press to connect directly at the pulley. Furthermore, as each bow is designed differently, it is often difficult to design a bow press that can adequately meet the needs of all various bow designs. Pulleys, wheels and cams, are also designed in such a varied fashion that at a time it was incomprehensible to apply a bow press, or any functioning element, at, on, or through the pulley.
It is therefore an object of the present invention to provide an portable compound bow press and tensioning device that can apply pressure as necessary to the pulley axle without coupling to the bowstring;
It is another object of the present invention to provide a bow press that handles the varying torsional forces on bow limbs to provide for increased stability of the system;
It is still another object of the present invention to provide a light weight and compact bow press;
It is yet another object of the present invention to provide an inexpensive bow press that can be manufactured easily;
It is still yet an object of the present invention to provide a portable bow press that is simple to operate and intuitive to use;
It is a further object of the present invention to provide a portable bow press that can be easily applied and disengaged from a compound bow limb section.